There is a very serious risk of accidents occurring in association with the loading and unloading of trucks and trailer, when such loading/unloading is carried out by means of fork-lift trucks at a loading dock or loading bay. In such cases, a fork-lift truck may be driven onto the loading bed of the truck or trailer through a swingable ramp or leveller that is normally anchored at the loading dock. The truck and its load often weighs several tons and there is an apparent risk that a vehicle that is only blocked with its parking brake will be displaced just in association with driving onto the truck bed or the ramp. Naturally, the risk of sliding is greater during wintertime when the vehicle wheels may be positioned on snow or ice. However, loose gravel on asphalt may have the same effect during other seasons. Such an unintentional displacement of a truck when driving onto it may have very serious consequences, since there is a risk of the fork-lift truck overturning or partly or completely falling down between the loading dock and the vehicle.
Traditionally, road freight vehicles and/or their load carriers (such as trailers or semi-trailers) are therefore secured in position at a loading dock through chocking by means of loose wedges or chocks that are positioned in front of one or several wheels of the vehicle or load carrier. An example of such a manual chocking is disclosed in U.S. Pat. No. 6,336,525 B1. Such traditional chocking suffers from many drawbacks. On the one hand, it involves that the vehicle driver has to go round and manually position and secure chocks against the vehicle wheels and that the safety is therefore completely dependent upon the driver performing the chocking in the appropriate manner. A chock that is not properly driven in under the wheel may easily come loose and simply be pushed ahead in front of the wheel. Moreover, no immediate indication is given to the forklift driver, neither regarding the fact that chocking has really been performed nor whether it has been properly performed. It is also known to secure or restrain vehicles by means of straps or chains, but these methods are both complex and unsafe.
Fixed devices have also been developed for blocking one or several vehicle wheels in association with loading and unloading. These known devices include those that are rigidly connected to the driveway or truck parking surface—see e.g. DE 44 27 406; EP 0 937 669 A1; EP 1 120 371; U.S. Pat. Nos. 6,371,253 B1; and 5,531,557—or that are alternatively embedded in said driveway or truck parking surface, see e.g. EP 0 580 415 A1; and U.S. Pat. No. 5,553,987. The first mentioned variant inevitably causes problems in association with snow clearance work etc. Furthermore, it may easily become blocked or even damaged in case the road freight vehicle is maneuvered so that it assumes an incorrect position on the device. This means that in these cases fairly high precision is required when backing the road freight vehicle up to the loading dock. The last mentioned variant involves very high costs, partly on account of the fact that its design is relatively complex and expensive and partly since it requires that an accommodating space is formed in the truck parking surface and is appropriately drained.
Finally U.S. Pat. No. 5,743,697 describes a wheel chocking apparatus that is indeed supported at the front of the loading dock, facing the vehicle, but that likewise, in all positions, interferes essentially with the driveway or truck parking surface and is an obstacle to snow clearance and other maintenance work at the parking surface. It is moreover intended to be introduced between the wheels of one wheel axle of the road freight vehicle in association with backing the vehicle up toward the loading dock Since it has a fixed width, it requires high precision during backing, and in addition thereto it does not permit any substantive variations in the axle width or track of the road freight vehicles.